The present invention relates to a data recording medium on which optical data may be recorded, for example, by focusing a laser beam on a radiation-sensitive recording layer to form a pit in the recording layer and from which the recorded optical data may be read out; and to a manufacturing method therefor.
A conventional data recording medium of this type (to be referred to as a record for brevity hereinafter) has, as shown in FIG. 1, a pair of disc-shaped transparent substrates 2 opposing each other with a spacer 1 interposed therebetween, and radiation-sensitive recording layers 3 each formed on the opposing surface of these substrates. A record of this construction has a space 4 between the recording layers 3 and has a weak mechanical strength. Therefore, the substrates 2 may be easily indented by an external mechanical pressure. When the record is left to stand obliquely, the record may bend by its own weight. When the record is transported to a place where the temperature difference is great, the air within the space expands or contracts and the substrates may be deformed due to the temperature difference between the space 4 and the outer atmosphere. The undulations or deflections thus formed result in a change in a spot size of the laser beam which becomes incident on the recording layer 3, and the data may not be written or read out satisfactorily. When a record is transferred from a place at high temperature and humidity to a place at low temperature, condensate forms within the space 4 and becomes attached to the recording layer, thus degrading the recording layer 3 at an early stage.
Also, where the substrate 2 is formed of a plastic material, water in the atmosphere permeates into the plastic substrate because a plastic material is high in water permeability. Thus, the water is attached to the recording layer 3, leading to deterioration of the recording layer in a short time.